Structural insights into AVR-Rmg8 recognition mechanisms by the wheat blast resistance gene Rmg8

Wheat blast disease, caused by the Triticum pathotype of Magnaporthe oryzae (MoT), poses a significant threat to global food security. The blast resistance gene Rmg8, recently isolated from a hexaploid wheat cultivar, strongly confers resistance to all Bangladeshi and Zambian MoT isolates that carry the eI type of AVR-Rmg8. However, the molecular interactions underlying this recognition at the protein level remain poorly understood. In this study, we elucidated the structural and biological characteristics of RMG8 proteins and their recognition of the AVR-Rmg8 effector proteins using computational biology approaches. Amino acid sequence comparison of four AVR-Rmg8 types revealed that only three amino acid residues distinguish the eI type of AVR-Rmg8, which induces a higher level of resistance conferred by RMG8. The most intriguing finding of this study is that only the eI type effector interacts with ATP through the Pro26 residue, a feature not present in the other AVR-Rmg8 types. We identified that the Protein Kinase C (PKC) domain of RMG8, where proline dependency mediates the phosphorylation of a serine residue, is involved in the strong recognition of the eI type of AVR-Rmg8. Phylogenetic analyses indicated that RMG8 might have evolved from proteins closely associated with plant signaling pathways. Although Rmg8 is an atypical resistance gene, our data suggest that it may function as a hub in the plant defense network, as it is a type of nuclear membrane protein, specifically a calcium-dependent multiple C2 domain protein with transmembrane regions (MCTP) kinase, which integrates signaling for effector recognition. Taken together, our study provides detailed insights into the molecular recognition mechanism between AVR-Rmg8 and RMG8, which is expected to aid in wheat blast resistance breeding. Future studies involving the purification and structural characterization of MoT effector proteins and Rmg8 gene products are necessary to validate these findings.